1. Field of the Invention
The present invention relates to a wheel rotation detecting device which detects the rotation speed (or rotation number) of a wheel of a car supported on a suspension and also detects the conditions of a rolling bearing unit portion supporting the wheel of the car, such as the temperature or vibration thereof.
2. Description of the Related Art
To obtain the rotation speed of a wheel in order to be able to control an antilock brake system (ABS) or a traction control system (TCS), in the related art, there are known various kinds of wheel supporting rolling bearing units with a rotation speed detecting device each structured such that a rotation speed detecting device is incorporated into a rolling bearing unit used to support the wheel on a suspension of a car. Here, as an example of a wheel supporting rolling bearing unit with a rotation speed detecting device which is used for the above purpose, FIG. 19 shows a wheel supporting rolling bearing unit which is disclosed in Japanese Patent No. 2838701.
An outer ring 1, which corresponds to a stationary ring, is supported on a knuckle forming a suspension by an outward-facing-flange-shaped mounting portion 2 formed on the outer peripheral surface of the outer ring 1 and, even when the rolling bearing unit is in use, the outer ring 1 is not rotatable. A rotary ring 3 is disposed on the inside diameter side of the outer ring 1; and, the rotary ring 3 is structured such that an inner ring 5 is fitted into and fixed to the inner end portion of a hub 4 (here, the term “inner side with respect to the axial direction” means the width-direction central side of the rolling bearing unit with respect to a car; and, in FIGS. 1, 14 and 19, on the right side). Between outer ring raceways 6, 6, which are formed in the inner peripheral surface of the outer ring 1 and respectively serve as stationary side raceways, and inner ring raceways 7, 7 which are formed in the outer peripheral surface of the hub 4 and inner ring 5 and respectively serve as rotary side raceways, there are interposed two rows of rolling elements, that is, balls 8, 8 each row including a plurality of rolling elements in such a manner that they are rollable while they are held by their respective retainers 9, 9.
The above-structured rotary ring 3 is rotatably supported on the inside diameter side of the outer ring 1. On the outer end portion (here, the term “outer side with respect to the axial direction” means the width-direction end portion side of the rolling bearing unit with respect to a car; and, in FIGS. 1, 14 and 19, on the left side) of the hub 4 forming the rotary ring 3, there is disposed a flange 10 which is used to support a wheel (not shown). Also, seal rings 11, 11 are interposed between the inner peripheral surfaces of the two end portions of the outer ring 1 and the middle portion outer peripheral surface of the hub 4 and the outer peripheral surface of the inner end portion of the inner ring 5; and, these seal rings 11, 11 shut off a space 12, in which the balls 8, 8 are disposed, from the outside, thereby being able to prevent grease enclosed in the space 12 from leaking out therefrom to the outside, and also to prevent a foreign substance floating in the outside from moving into the space 12.
Also, an encoder 13 is fitted with and fixed to the outside of the middle portion of the hub 4, namely, the portion extending between the two rows of balls 8, 8 in an interference fit manner. The encoder 13 is formed of magnetic metal material such as soft steel into a circular-ring shape; and, on the outer peripheral surface of the encoder 13, there are formed gear-shaped uneven portions (composed of recessed portions and projected portions) to thereby cause the magnetic characteristics of the present outer peripheral surface to vary alternately and at regular intervals with respect to the circumferential direction. On the other hand, in the middle portion of the outer ring 1, a rotation detecting sensor 14 is inserted into and supported by a mounting hole 15 which is formed in such a manner that it can bring the inner and outer peripheral surfaces of the outer ring 1 into communication with each other; and, a detecting portion, which is formed in the leading end face (in FIG. 19, the lower end face) of the rotation detecting sensor 14, is disposed near to and opposed to the outer peripheral surface of the encoder 13.
When the above-structured wheel supporting rolling bearing unit with a rotation speed detector of the related art is in use while it is assembled between the suspension and wheel, in case where this wheel is rotated, the recessed portions and projected portions existing on the outer peripheral surface of the encoder 13 pass alternately through the detecting surface of the rotation detecting sensor 14. As a result of this, the density of magnetic flux flowing in the rotation detecting sensor 14 varies, whereby the output of the rotation detecting sensor 14 varies. A frequency, at which the output varies, is in proportion to the rotation speed of the wheel and, therefore, in case where the output signal of the rotation detecting sensor 14 is sent to a control unit (not shown), the ABS or TCS can be controlled properly. Also, the rotation number of the wheel can be obtained from the number of times of the variations of the output of the rotation detecting sensor 14. Thanks to this, recently, the output signal of the rotation detecting sensor 14 has been used as a signal to control not only the ABS and TCS but also a car navigation system and an ITS (Intelligent Transport System).
In the case of the above-mentioned wheel supporting rolling bearing unit with a rotation speed detector of the related art, the rotation speed and rotation number of the wheel can be detected but the other conditions of the wheel supporting rolling bearing unit cannot be detected. On the other hand, due to the rapid progress of a car technology in recent years, there arises the need to obtain more pieces of information from the wheel supporting rolling bearing unit.
For example, in case where it is possible to know the temperature of a wheel supporting rolling bearing unit portion of a car, an increase in the temperature of the wheel supporting rolling bearing unit portion and the overheated condition of a brake portion of a car can be detected. The increase in the temperature of the wheel supporting rolling bearing unit portion not only provides important data in knowing the life of the present wheel supporting rolling bearing unit itself but also can show the overheated condition of the brake portion to thereby give a warning to a driver before a dangerous condition such as vapor lock occurs. By the way, in case where a speed signal from a rotation detecting sensor is combined with a temperature signal from a temperature sensor, generation of heat due to the friction loss of the present rolling bearing unit can be corrected. Therefore, even in a moving body such as a vehicle in which the temperature always varies according to variations in the rotation speed, the accuracy of detection of the temperature in the abnormality of the present rolling bearing unit can be enhanced. Also, by measuring the magnitude of the vibrations and the wavelengths of the wheel supporting rolling bearing unit portion and by analyzing the frequencies thereof, there can be obtained important data in knowing the life of the wheel supporting rolling bearing unit in addition to the conditions of the road surfaces and the conditions of the air pressures of tires. In case where proper knowledge of the road conditions is obtained, the automatic change of the damping force of a damper attached to the suspension can be executed properly; and, in case where the tire air pressure can be estimated, it is possible not only to give a warning when the tire air pressure is abnormal but also to increase or decrease the tire air pressure. This can prevent an accident such as tire burst which may occur when a vehicle runs at a high speed with a low tire air pressure. Further, a proper knowledge of the life of the wheel supporting rolling bearing unit can tell the driver the remaining life thereof before the car becomes impossible to run any further and thus can give a warning to the driver in such a condition that the driver can drive the car up to a garage.
To know the above-mentioned temperatures and vibrations, a temperature sensor and a vibration sensor (an acceleration sensor) may be assembled to a portion of the wheel supporting rolling bearing unit. However, in case where these sensors are assembled independently of the rotation detecting sensor, the weight and assembling space of the wheel supporting rolling bearing unit increase, and the number of assembling man-hour increases to thereby increase the manufacturing cost of the car unfavorably.